There have been known electrophotographic image forming apparatuses using a two-component developer containing toner and carrier having a magnetic component. Such image forming apparatuses are designed such that an electrostatic latent image corresponding to image data is formed on a surface of a photoreceptor and the electrostatic latent image is developed and made visible by toner. In this process, the two-component developer containing toner and carrier is carried to a position facing the surface of the photoreceptor, and the toner is transferred to the electrostatic latent image by an electrostatic attracting force which is exerted by the electrostatic latent image and which is stronger than adhesion (adhesive force) between the toner and the carrier.
It is known that in a developing process using the two-component developer, specific charge of toner, the shape of toner etc. have an influence on adhesion between toner and carrier. Further, it is known that the electrostatic property of toner deteriorates as time passes.
If the adhesion between toner and carrier drops, there occur inconveniences such as drop in image quality due to excessive amount of toner transferring from a developing device to a photoreceptor, and scattering of toner from the developing device.
As such, in view of development of toner for a two-component developer, optimization of toner for a developing process, evaluation of drop in toner quality etc., there has been requested a technique of easily and accurately measuring adhesion between toner and carrier or distribution of the adhesion therebetween.
In general, adhesion of powder such as toner is detected by measuring a strength required to separate the powder from a material to which the powder is attached. Known examples of a method for separating powder from a material include centrifugation, use of an electric field, and blowing.
In cases of centrifugation (see Patent Literatures 1-3 for example), there are provided a sample substrate which is positioned in a rotor of a centrifugal separator and to which powder is attached and a receiving substrate which is positioned to face the sample substrate and which receives powder separated from the sample substrate. Powder is separated from the sample substrate by a centrifugal force derived from rotation of the rotor and the powder is attached to the receiving substrate. Then, the mass of the powder attached to the receiving substrate is measured, the centrifugal force required is calculated based on the mass of the powder and the number of rotation of the rotor, and adhesion of the powder attaching to the sample substrate is calculated.
In cases of use of an electric field (see Patent Literatures 4-6 for example), there are provided a conductive sample substrate to which powder is attached and a conductive receiving substrate which is positioned to face the conductive sample substrate and which receives powder separated from the sample substrate. An electric field is applied across an electrode positioned at the sample substrate and an electrode positioned at the receiving substrate, so that charged powder is separated from the sample substrate and attached to the receiving substrate. Then, the mass of the powder attached to the receiving substrate is measured, and an electrostatic force required for the separation is calculated based on the measured mass, electrical charges of powder measured in advance, and the strength of the applied electric field. Thus, adhesion of powder attaching to the sample substrate is calculated.
In cases of blowing (see Patent Literature 2 for example), compressed air is jet at a predetermined speed toward a sample substrate to which powder is attached so that the powder is separated from the sample substrate, the separated powder is collected by a dust collector, air resistance of the powder is calculated based on a volume of the powder collected by the dust collector, and adhesion of powder attaching to the sample substrate is calculated based on the air resistance.
Further, Patent Literature 7 discloses that a sample substrate to which powder is attached is moved at a high speed so as to separate the powder from the sample substrate and adhesion of the powder attaching to the sample substrate is detected based on the number of particles and the mass of the particles just after the separation.
Further, Patent Literature 8 discloses that a developer made of a mixture of toner and carrier is magnetically attached to a sample substrate and the sample substrate is moved at a high speed in a direction perpendicular to a surface of the sample substrate while applying a predetermined electric field on the developer so that toner is separated from carrier, and the number of particles and a mass of the particles just after the separation are calculated so as to measure adhesion between toner and carrier.